1. Technical Field
The present invention relates to a locking system for electrode joints. More particularly, the invention concerns a unique system for facilitating the mechanical locking of electrode joints using an adhesive material.
2. Background Art
Graphite electrodes are used in the steel industry to melt the metals and other ingredients used to form steel in electrothermal furnaces. The heat needed to melt metals is generated by passing current through one or a plurality of electrodes, usually three, and forming an arc between the electrodes and the metal. Electrical currents in excess of 100,000 amperes are often used. The resulting high temperature melts the metals and other ingredients. Generally, the electrodes used in steel furnaces are used in electrode columns, that is, a series of individual electrodes joined to form a single column. In this way, as electrodes are depleted during the thermal process, replacement electrodes can be joined to the column to maintain the length of the column extending into the furnace.
Conventionally, electrodes are joined into columns via a pin (sometimes referred to as a nipple) that functions to join the ends of adjoining electrodes. Typically, the pin takes the form of opposed male threaded sections, with at least one end of each of the electrodes comprising female threaded sections capable of mating with a male threaded section of the pin. Thus, when each of the opposing male threaded sections of a pin are threaded into female threaded sections in the ends of two electrodes, those electrodes become joined into an electrode column. Commonly, the joined ends of the adjoining electrodes, and the pin therebetween, are referred to in the art as a joint.
Alternatively, the electrodes can be formed with a male threaded protrusion or tang machined into one end and a female threaded socket machined into the other end, such that the electrodes can be joined by threading the male tang of one electrode into the female socket of a second electrode, and thus form an electrode column. The joined ends of two adjoining electrodes in such an embodiment is referred to in the art as a male-female joint.
Given the extreme thermal and mechanical stress that the electrode and the joint (and indeed the electrode column as a whole) undergo, detachment of the joint and subsequent loss of the electrode column below the detached joint is a recurring problem. In so-called non-jammed joints, where the threads of the pin and electrodes, or the two electrodes in a male-female joint, meet on only one of the thread faces, solutions have been proposed, where pitch or another material is allowed to melt and then infiltrate between the threads, where it carbonizes in the heat of the furnace and forms a bond between the joint elements.
For instance, in International application PCT/US02/10125, inventors Pavlisin and Weber disclose a “plug” formed of pitch and expandable graphite. When the plug is placed at the base of an electrode socket, the heat of the furnace causes the pitch to melt and the graphite to expand, forcing the melted pitch between the threads where it carbonizes and locks the joint together. Another joint locking system employed in the past has been to provide one or more holes in an electrode pin at or near each of its ends, and positioning pitch in the holes. Again, the heat of the furnace causes the pitch to melt and flow across the threads where it carbonizes and locks the joint in position.
Although effective, these prior art methods for joint locking are only maximally effective in non-jammed threads, such as are illustrated in FIG. 1a. In fully jammed threads, illustrated in FIG. 1, where both faces of the threads of one element contact the threads of the other element, there is insufficient space between the threads to permit the pitch or other adherent composition to flow between the threads. There exists a need, therefore, for an improved locking mechanism for fully jammed graphite electrode joints.